Soap-Making Manual Part 2

The red oil, sometimes called saponified red oil, is often semi-solid, resembling a soft tallow, due to the presence of stearic acid. The distilled oils are usually clear, varying in color from light to a deep brown. Stearic acid, which reaches the trade in slab form, varies in quality from a soft brown, greasy, crumbly solid of unpleasant odor to a snow white, wax-like, hard, odorless ma.s.s. The quality of stearic acid is best judged by the melting point, since the presence of any oleic acid lowers this. The melting point of the varieties used in soap manufacture usually ranges from 128 to 132 F. Red oil is used in the manufacture of textile soaps, replacing olive oil foots soap for this purpose, chlorophyll being used to color the soap green. Stearic acid, being the hard firm fatty acid, may be used in small quant.i.ties to give a better grade of soap body and finish. In adding this substance it should always be done in the crutcher, as it will not mix in the kettle.

It finds its largest use for soap, however, in the manufacture of shaving soaps and shaving creams, since it produces the non-drying creamy lather so greatly desired for this purpose. Both red oil and stearic acid being fatty acids, readily unite with the alkali carbonates, carbon dioxide being formed in the reaction and this method is extensively used in the formation of soap from them.

RANCIDITY OF OILS AND FATS.

Rancidity in neutral oils and fats is one of the problems the soap manufacturer has to contend with. The mere saying that an oil is rancid is no indication of its being high in free acid. The two terms rancidity and acidity are usually allied. Formerly, the acidity of a fat was looked upon as the direct measure of its rancidity. This idea is still prevalent in practice and cannot be too often stated as incorrect. Fats and oils may be _acid_, or _rancid_, or _acid and rancid_. In an acid fat there has been a hydrolysis of the fat and it has developed a rather high percentage of free acid. A rancid fat is one in which have been developed compounds of an odoriferous nature. An acid and rancid fat is one in which both free acid and organic compounds of the well known disagreeable odors have been produced.

It cannot be definitely stated just how this rancidity takes place, any more than just what are the chemical products causing rancidity. The only conclusion that one may draw is that the fats are first hydrolyzed or split up into glycerine and free fatty acids. This is followed by an oxidation of the products thus formed.

Moisture, air, light, enzymes (organized ferments) and bacteria are all given as causes of rancidity.

It seems very probable that the initial splitting of the fats is caused by enzymes, which are present in the seeds and fruits of the vegetable oils and tissue of animal fats, in the presence of moisture. Lewkowitsch strongly emphasizes this point and he is substantiated in his idea by other authorities. Others hold that bacteria or micro-organisms are the cause of this hydrolysis, citing the fact that they have isolated various micro-organisms from various fats and oils. The acceptance of the bacterial action would explain the various methods of preservation of oils and fats by the use of antiseptic preparations. It cannot, however, be accepted as a certainty that bacteria cause the rancidity of fats.

The action of enzymes is a more probable explanation.

The hydrolysis of fats and oils is accelerated when they are allowed to remain for some time in the presence of organic non-fats. Thus, palm oil, lower grades of olive oil, and tallow, which has been in contact with the animal tissue for a long time, all contain other nitrogenous matter and exhibit a larger percentage of free fatty acid than the oils and fats not containing such impurities.

Granting this initial splitting of the fat into free fatty acids and glycerine, this is not a sufficient explanation. The products thus formed must be acted upon by air and light. It is by the action of these agents that there is a further action upon the products, and from this oxidation we ascertain by taste and smell (chemical means are still unable to define rancidity) whether or not a fat is rancid. While some authorities have presumed to isolate some of these products causing rancidity, we can only a.s.sume the presence of the various possible compounds produced by the action of air and light which include oxy fatty acids, lactones, alcohols, esters, aldehydes and other products.

The soap manufacturer is interested in rancidity to the extent of the effect upon the finished soap. Rancid fats form darker soaps than fats in the neutral state, and very often carry with them the disagreeable odor of a rancid oil. Further, a rancid fat or oil is usually high in free acid. It is by no means true, however, that rancidity is a measure for acidity, for as has already been pointed out, an oil may be rancid and not high in free acid.

The percentage of free fatty acid is of even greater importance in the soap industry. The amount of glycerine yield is dependent upon the percentage of free fatty acid and is one of the criterions of a good fat or oil for soap stock.

PREVENTION OF RANCIDITY.

Since moisture, air, light and enzymes, produced by the presence of organic impurities, are necessary for the rancidity of a fat or oil, the methods of preventing rancidity are given. Complete dryness, complete purification of fats and oils and storage without access of air or light are desirable. Simple as these means may seem, they can only be approximated in practice. The most difficult problem is the removal of the last trace of moisture. Impurities may be lessened very often by the use of greater care. In storing it is well to store in closed barrels or closed iron tanks away from light, as it has been observed that oils and fats in closed receptacles become rancid less rapidly than those in open ones, even though this method of storing is only partially attained.

Preservatives are also used, but only in edible products, where their effectiveness is an open question.

CHEMICAL CONSTANTS OF OILS AND FATS.

Besides the various physical properties of oils and fats, such as color, specific gravity, melting point, solubility, etc., they may be distinguished chemically by a number of chemical constants. These are the iodine number, the acetyl value, saponification number, Reichert-Meissl number for volatile acids, Hehner number for insoluble acids. These constants, while they vary somewhat with any particular oil or fat, are more applicable to the edible products and are criterions where any adulteration of fat or oil is suspected. The methods of carrying out the a.n.a.lyses of oils and fats to obtain these constants are given in the various texts[2] on oils and fats, and inasmuch as they are not of great importance to the soap industry they are merely mentioned here.

OIL HARDENING OR HYDROGENATING.

It is very well known that oils and fats vary in consistency and hardness, depending upon the glycerides forming same. Olein, a combination of oleic acid and glycerine, as well as oleic acid itself largely forms the liquid portion of oils and fats. Oleic acid (C_{18}H_{34}O_{2}) is an unsaturated acid and differs from stearic acid (C_{18}H_{36}O_{2}), the acid forming the hard firm portion of oils and fats, by containing two atoms of hydrogen less in the molecule.

Theoretically it should be a simple matter to introduce two atoms of hydrogen into oleic acid or olein, and by this mere addition convert liquid oleic acid and olein into solid stearic acid and stearine.

For years this was attempted and all attempts to apply the well known methods of reduction (addition of hydrogen) in organic chemistry, such as treatment with tin and acid, sodium amalgam, etc., were unsuccessful.

In recent years, however, it has been discovered that in the presence of a catalyzer, nickel in finely divided form or the oxides of nickel are usually employed, the process of hydrogenating an oil is readily attained upon a practical basis.

The introduction of hardened oils has opened a new source of raw material for the soap manufacturer in that it is now possible to use oils in soap making which were formerly discarded because of their undesirable odors. Thus fish or train oils which had up to the time of oil hydrogenating resisted all attempts of being permanently deodorized, can now be employed very satisfactorily for soap manufacture. A j.a.panese chemist, Tsujimoto[3] has shown that fish oils contain an unsaturated acid of the composition C_{18}H_{28}O_{2}, for which he proposed the name clupanodonic acid. By the catalytic hardening of train oils this acid pa.s.ses to stearic acid and the problem of deodorizing these oils is solved.[4]

At first the introduction of hardened oils for soap manufacture met with numerous objections, due to the continual failures of obtaining a satisfactory product by the use of same. Various attempts have now shown that these oils, particularly hardened train oils, produce extraordinarily useful materials for soap making. These replace expensive tallow and other high melting oils. It is of course impossible to employ hardened oils alone, as a soap so hard would thus be obtained that it would be difficultly soluble in water and possess very little lathering quality. By the addition of 20-25% of tallow oil or some other oil forming a soft soap a very suitable soap for household use may be obtained. Ribot[5] discusses this matter fully. Hardened oils readily saponify, may be perfumed without any objections and do not impart any fishy odor to an article washed with same. Meyerheim[6] states that through the use of hydrogenated oils the hardness of soap is extraordinarily raised, so that soap made from hardened cottonseed oil is twelve times as hard as the soap made from ordinary cottonseed oil.

This soap is also said to no longer spot yellow upon aging, and as a consequence of its hardness, is able to contain a considerably higher content of rosin through which lathering power and odor may be improved.

Hardened oils can easily be used for toilet soap bases, provided they are not added in too great a percentage.

The use of hardened oils is not yet general, but there is little doubt that the introduction of this process goes a long way toward solving the problem of cheaper soap material for the soap making industry.

GREASE.

Grease varies so greatly in composition and consistency that it can hardly be cla.s.sed as a distinctive oil or fat. It is obtained from refuse, bones, hides, etc., and while it contains the same const.i.tuents as tallow, the olein content is considerably greater, which causes it to be more liquid in composition. Grease differs in color from an off-white to a dark brown. The better qualities are employed in the manufacture of laundry and chip soap, while the poorer qualities are only fit for the cheapest of soaps used in scrubbing floors and such purposes. There is usually found in grease a considerable amount of gluey matter, lime and water. The percentage of free fatty acid is generally high.

The darker grades of grease are bleached before being used. This is done by adding a small quant.i.ty of sodium nitrate to the melted grease and agitating, then removing the excess saltpeter by decomposing with sulphuric acid. A better method of refining, however, is by distillation. The chrome bleach is also applicable.

ROSIN (COLOPHONY, YELLOW ROSIN, RESINA).

Rosin is the residue which remains after the distillation of turpentine from the various species of pines. The chief source of supply is in the States of Georgia North and South Carolina. It is a transparent, amber colored hard pulverizable resin. The better grades are light in color and known as water white (w. w.) and window gla.s.s (w. g.). These are obtained from a tree which has been tapped for the first year. As the same trees are tapped from year to year, the product becomes deeper and darker in color until it becomes almost black.

The const.i.tuents of rosin are chiefly (80-90%) abietic acid or its anhydride together with pinic and sylvic acids. Its specific gravity is 1.07-1.08, melting point about 152.5 C., and it is soluble in alcohol, ether, benzine, carbon disulfide, oils, alkalis and acetic acid. The main use of rosin, outside of the production of varnishes, is in the production of laundry soaps, although a slight percentage acts as a binder and fixative for perfumes in toilet soaps and adds to their detergent properties. Since it is mainly composed of acids, it readily unites with alkaline carbonates, though the saponification is not quite complete and the last portion must be completed through the use of caustic hydrates, unless an excess of 10% carbonate over the theoretical amount is used. A lye of 20 B. is best adapted to the saponification of rosin when caustic hydrates are employed for this purpose, since weak lyes cause frothing. While it is sometimes considered that rosin is an adulterant for soap, this is hardly justifiable, as it adds to the cleansing properties of soap. Soaps containing rosin are of the well known yellowish color common to ordinary laundry soaps. The price of rosin has so risen in the last few years that it presents a problem of cost to the soap manufacturer considering the price at which laundry soaps are sold.

ROSIN SAPONIFICATION.

As has been stated, rosin may be saponified by the use of alkaline carbonates. On account of the possibility of the soap frothing over, the kettle in which the operation takes place should be set flush with the floor, which ought to be constructed of cement. The kettle itself is an open one with round bottom, equipped with an open steam coil and skimmer pipe, and the open portion is protected by a semi-circular rail. A powerful grid, having a 3-inch mesh, covers one-half of the kettle, the sharp edges protruding upwards.

The staves from the rosin casks are removed at the edge of the kettle, the rosin placed on the grid and beaten through with a hammer to break it up into small pieces.

To saponify a ton of rosin there are required 200 lbs. soda ash, 1,600 lbs. water and 100 lbs. salt. Half the water is run into the kettle, boiled, and then the soda ash and half the salt added. The rosin is now added through the grid and the mixture thoroughly boiled. As carbon dioxide is evolved by the reaction the boiling is continued for one hour to remove any excess of this gas. A portion of the salt is gradually added to grain the soap well and to keep the ma.s.s in such condition as to favor the evolution of gas. The remainder of the water is added to close the soap and boiling continued for one or two hours longer. At this point the kettle must be carefully watched or it will boil over through the further escape of carbon dioxide being hindered. The ma.s.s, being in a frothy condition, will rapidly settle by controlling the flow of steam. The remaining salt is then scattered in and the soap allowed to settle for two hours or longer. The lyes are then drained off the top. If the rosin soap is required for toilet soaps, it is grained a second time. The soap is now boiled with the water caused by the condensation of the steam, which changes it to a half grained soap suitable for pumping. A soap thus made contains free soda ash 0.15% or less, free rosin about 15%. The ma.s.s is then pumped to the kettle containing the soap to which it is to be added at the proper stage. The time consumed in thus saponifying rosin is about five hours.

NAPHTHENIC ACIDS.

The naphtha or crude petroleum of the various provinces in Europe, as Russia, Galacia, Alsace and Roumania yield a series of bodies of acid character upon refining which are designated under the general name of naphthenic acids. These acids are retained in solution in the alkaline lyes during the distillation of the naphtha in the form of alkaline naphthenates. Upon adding dilute sulphuric acid to these lyes the naphthenates are decomposed and the naphthenic acids float to the surface in an oily layer of characteristic disagreeable odor and varying from yellow to brown in color[7]. In Russia particularly large quant.i.ties of these acids are employed in the manufacture of soap.

The soaps formed from naphthenic acids have recently been investigated[8] and found to resemble the soaps made from cocoanut oil and palm kernel oil, in that they are difficult to salt out and dissociate very slightly with water. The latter property makes them valuable in textile industries when a mild soap is required as a detergent, e. g., in the silk industry. These soaps also possess a high solvent power for mineral oils and emulsify very readily. The mean molecular weight of naphthenic acids themselves is very near that of the fatty acids contained in cocoanut oil, and like those of cocoanut oil a portion of the separated acids are volatile with steam. The iodine number indicates a small content of unsaturated acids.

That naphthenic acids are a valuable soap material is now recognized, but except in Russia the soap is not manufactured to any extent at the present time.

ALKALIS.

The common alkali metals which enter into the formation of soap are sodium and pota.s.sium. The hydroxides of these metals are usually used, except in the so called carbonate saponification of free fatty acids in which case sodium and pota.s.sium carbonate are used. A water solution of the caustic alkalis is known as lye, and it is as lyes of various strengths that they are added to oils and fats to form soap. The density or weight of a lye is considerably greater than that of water, depending upon the amount of alkali dissolved, and its weight is usually determined by a hydrometer. This instrument is graduated by a standardized scale, and while all hydrometers should read alike in a liquid of known specific gravity, this is generally not the case, so that it is advisable to check a new hydrometer for accurate work against one of known accuracy. In this country the Baume scale has been adopted, while in England a different graduation known as the Twaddle scale is used. The strength of a lye or any solution is determined by the distance the instrument sinks into the solution, and we speak of the strength of a solution as so many degrees Baume or Twaddle which are read to the point where the meniscus of the lye comes on the graduated scale. Hydrometers are graduated differently for liquids of different weights. In the testing of lyes one which is graduated from 0 to 50 B.

is usually employed.

_Caustic soda_ is received by the consumer in iron drums weighing approximately 700 lbs. each. The various grades are designated as 60, 70, 74, 76 and 77%. These percentages refer to the percentage of sodium oxide (Na_{2}O) in 100 parts of pure caustic soda formed by the combination of 77-1/2 parts of sodium oxide and 22-1/2 parts of water, 77-1/2% being chemically pure caustic soda. There are generally impurities present in commercial caustic soda. These consist of sodium carbonate, sodium chloride or common salt and sometimes lime. It is manufactured by treating sodium carbonate in an iron vessel with calcium hydroxide or slaked lime, or by electrolysis of common salt. The latter process has yet been unable to compete with the former in price.

Formerly all the caustic soda used in soap making was imported, and it was only through the American manufacturer using a similar container to that used by foreign manufacturers that they were able to introduce their product. This prejudice has now been entirely overcome and most of the caustic soda used in this country is manufactured here.

CAUSTIC POTASH.

The output of the salts containing pota.s.sium is controlled almost entirely by Germany. Formerly the chief source of supply of pota.s.sium compounds was from the burned ashes of plants, but about fifty years ago the inexhaustible salt mines of Sta.s.sfurt, Germany, were discovered.

The salt there mined contains, besides the chlorides and sulphates of sodium, magnesium, calcium and other salts, considerable quant.i.ties of pota.s.sium chloride, and the Sta.s.sfurt mines at present are practically the entire source of all pota.s.sium compounds, in spite of the fact that other localities have been sought to produce these compounds on a commercial basis, especially by the United States government.

After separating the pota.s.sium chloride from the magnesium chloride and other substances found in Sta.s.sfurt salts the methods of manufacture of caustic potash are identical to those of caustic soda. In this case, however, domestic electrolytic caustic potash may be purchased cheaper than the imported product and it gives results equal to those obtained by the use of the imported article, opinions to the contrary among soap makers being many. Most of the caustic potash in the United States is manufactured at Niagara Falls by the Niagara Alkali Co., and the Hooker Electrochemical Co., chlorine being obtained as a by-product. The latter concern employs the Townsend Cell, for the manufacture of electrolytic potash, and are said to have a capacity for making 64 tons of alkali daily.